.header {
  width: 100%;
  height: 70px;
  transition: all .4s ease-in-out;
  background-color: #fff;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 2000;
  margin: 0 -0.5%;
}

.header .logo {
  width: 146px;
  display: flex;
  align-items: center;
  margin-left: 1%;
}

.header .logo a {
  width: 100%;
  display: block;
  height: 70px;
  background-position: 0;
  background-repeat: no-repeat;
  background-size: 146px 26px;
  background-image: url("../images/logo.png");
}

.app {
  width: 100%;
  height: 100%;
  padding-top: 90px;
}

.app ul {
  flex-wrap: wrap;
}

.app ul li {
  flex: 0 0 19%;
  max-width: 19%;
  height: 180px;
  cursor: pointer;
  position: relative;
  background-size: cover;
  background-position: center;
  margin: 0 0.5%;
  margin-bottom: 1%;
  border-radius: 3px;
}

.app ul li:nth-child(5n) {
  margin-right: 0;
}

.app ul li img {
  width: 100%;
  border-radius: 3px;
}

.app ul li .layer {
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.6);
  position: absolute;
  left: 0;
  top: 0;
  transition: all 0.4s;
  opacity: 0;
  border-radius: 3px;
}

.app ul li .layer .btn {
  width: 50px;
  height: 50px;
  position: relative;
  z-index: 100;
}

.app ul li .layer .btn img {
  width: 100%;
  height: 100%;
}

.app ul li:hover .layer {
  opacity: 1;
}